Thoughts about the Cascadia Subduction Zone

There are geological processes at work 24/7, 365 days a year, all over dynamic planet Earth. As our Oregon Master Naturalist class assembled on the sands at Hug Point, we were asked to gaze out on the Pacific Ocean.

Al Niem, Oregon State University Emeritus Professor of Geosciences, instructed, “Look out at the horizon. What do you see?”

In response, a wave of thoughts flowed through our group… a good spot to fish, place for beautiful sunsets, where storms roll in, clouds... After allowing time for reflection, Al announced again, “Look at the horizon- That’s where the subducting plate boundary is!!”

An “aha” moment resulted … none of us will look out to sea again without that thought in mind. Al provided an impacting visual reminder that plate tectonics are at work close by … with forces that continuously shape the past, present, and future of life-sustaining systems on our planet. The subduction zone at Oregon’s front door is formed where the edge of the Juan De Fuca Plate is subducting into the mantle beneath the North American Plate.

Before our field trip to the beach, Bob Lillie, Oregon State University Emeritus Professor of Geosciences, explained the dynamics at work in the Cascadia Subduction Zone. He referred to this chart to illustrate how the Juan De Fuca Plate is converging with the North American Plate. The North American Plate is formed by continental crust which is thicker than the oceanic crust that forms the Juan De Fuca plate. The subducting plate boundary is the result where the oceanic crust slides beneath the continental crust. In the plate tectonics of the Pacific Northwest, this geologic configuration is known as the Cascadia Subduction Zone.

Diagram from Cascadia EarthScope Earthquake and Tsunami Education Program (CEETEP)

Although most volcanoes and earthquakes occur along plate boundaries, subduction zones are of extreme concern by geologists. This is where deeper earthquakes tend to occur. Experts say it’s not a matter of if; it’s a matter of when the Cascadia Subduction Zone will unleash earthquake forces strong enough to trigger a tsunami event along the Oregon coast.

Al and Bob prompted our OSU Master Naturalist cadre to think about what we would do in the event of an earthquake/tsunami occurrence. Students in the class who reside at the beach appeared confident that they would know how to react. I don’t live at the beach, and wasn’t so confident.

When looking out at the Pacific Ocean horizon, I would appreciate feeling more assured about having thought through the tsunami scenario… especially knowing the first 20-25 minutes are most critical for survival. Al cautioned, that reaction time starts ticking when the earthquake commences. While the shaking occurs, escape is delayed by “take cover, and hold.” Then… it’s paramount to maximize those precious escape minutes.

To prepare, I downloaded the TsunamiEvac – NW app on my cell phone. Click on the image for more information.

Oregon Department of Geology and Mineral Industries, in consultation with local officials., spent four years to map the entire Oregon coast to educate the public just how far inland a tsunami would come. A collection of 131 maps were created to show tsunami inundation zones. Two zones are depicted on area specific maps to illustrate (1) inundation in the event of a distant tsunami; and, (2) inundation in the event of a local tsunami, such as one originating from the Cascadia Subduction zone offshore. The maps also outline evacuation routes people can take to escape.

The maps are available for free in PDF format. Click on the map icon below. Scroll down the webpage for a list of evacuation map-links for specific Oregon coastal communities.

Next time I plan a visit, vacation, camping trip, or fishing excursion along the Oregon coast, it’s good to know I can scan the plan for the tsunami evacuation route written for where we are traveling. In Oregon… it may be more important than sunscreen!

Will the plans work? I don’t know, but the chances for helping others and survival should be improved if prior knowledge and preparation are applied. The dangers posed by the Cascadian Subduction Zone are real. When exactly communities will have to respond to the inundation of a tsunami, only Nature’s Geologic Clock can tell. After my weekend learning experience, I feel responsible to seek more information and to share these findings.

The forces are with us. Some will continue to leave us awestruck with their beauty; others will provide sobering testament to the power of Earth’s dynamic cycles.

There are more resources and information on the Oregon Tsunami Information Clearinghouse website: